Modern digital subscriber line (DSL) communication systems may have fixed connection rates. When an actual user data rate of a subscriber line is lower than its connection rate, a transmission system may add idle cells or codewords to keep a constant physical media dependent (PMD) transmission rate. As user traffic may be bursty on the subscriber line, the transmission of idle cells may sometimes consume relatively significant power in the transmission system.
Whether a data transmission unit (DTU) (sometimes also referred to as a data transfer unit) comprises user data or just idle cells, when a receiver detects an error or corruption, it may request retransmission. When the user data rate is low, potentially many idle cells may be inserted into a DTU, consequently power may be wasted on transmitting the idle cells. For example, in a DSL system, in case a discontinuous transmission mode is not utilized or not supported, idle DTUs (IDTUs) may be added to maintain a constant transmission frequency of discrete multi-tone (DMT) symbols.